Many devices require electrical power to operate, and controlling the devices during normal conditions, while providing for safety during abnormal conditions, is integral to proper device operation. For example, a typical factory often includes many machines (motors), linked together in operation, and linked to other devices, for handling items to be assembled and for handling tools or items carrying out or supporting the assembly. A typical factory often operates around the clock, twenty-four hours per day, seven days per week.
For safety purposes, the linked machines include an emergency stop (E-stop) switch for terminating electrical power to the machines in an emergency situation. While the design of an emergency stop device may vary, the device generally includes a switch which converts from a normal state to an emergency state when an emergency stop is necessary, the emergency state overriding all other robot controls to remove power from all electrically driven devices, causing all moving parts to stop, and to remove power from all other hazardous functions present in the safeguarded space without causing additional hazards.
Components controlling the devices during normal conditions, and the E-stop switches controlling (shutting down) operation during abnormal conditions, can become faulty. Fault conditions generally result from two causes: 1) a failed switch; and/or 2) an inadvertent hot wire. A failed switch usually results from a fused contact, often occurring after a rated contact current is exceeded. Because many power sources are not well regulated, current surges are not uncommon, therefore, fused contacts occasionally occur. Also, environmental conditions can affect contact surfaces, contributing to contact failure. If a contact in an E-stop switch, control circuit, or power relay becomes fused, there is often no way to know until the equipment becomes uncontrollable. Furthermore, an inadvertent (stray) hot wire can short circuit a switch, or provide power to a motor from an inadvertent source by bypassing a switch.
The ability to periodically inspect and/or test switch components, equipment control circuitry, and the E-stop switches, is a very important part of successful preventive maintenance plan, but such inspection/testing is not always possible, or at least not practical. Although there are no strict standards for the testing of E-stop switches and equipment control circuitry, most are not adequately tested because of the interference testing has with equipment operation.
For the foregoing reasons, there is a need for an E-stop device, and associated equipment control circuitry, allowing for testing of the control circuitry and E-stop switch, at anytime, while the equipment is in operation, or idle, without interfering with or prohibiting the capability of the E-stop switch to de-activate all energy sources to the equipment in the event of a mishap or accident.